Stability Analysis and Stabilization Solutions for Landslides (Case Study: Khorramabad-Pole Zaal Freeway)

As for the increasing construction of buildings, roads, railways and others in the mountainous areas and steep, stabilizing the natural and artificial slopes is more and more considered. There are innumerous methods for slope stabilization in which they are trying  to increase the resistant forces for driving forces. Therefore, the safety factor increases. The purpose of this study was to estimate the stability of dominant sliding slopes on the roads and the role of nailing and tracing on the stabilization of these slides on 40 km the Khorramabad-Pole Zaal freeway. In this research, at first, 8 sliding slopes along the roads were found. Using field study sampling and analysis of soil, topography and mining slope stability factor  domains, all the parameters of slope stability analysis, including cs: soil cohesion, cr: root cohesion, φ: internal friction angle of soil, γd: soil density and γw: wet density of soil, were entered these parameters in slope stability analysis software and the safety factor were determined for each slide. we can identify the unstable slopes by this method and determine the protection operations to increase stability factor, so that nailing action in slide 6 with very high vulnerability class, the location of 33° 20' 43" north latitude and 48° 10' 59" E increases the stability factor from 0.57 to 1.98 and the tracing mechanism in the slope, increases the stability or safety factor at the value 2.10. And finally we can determine the best way to do the protective mechanism.
Extended Abstract
1-Introduction
One of the main Ingredient stimulater of landslides, road construction, which is the basis for the large landslides by creating unstable trenches on both sides of the road, changing the course of rivers, unloading and loading unsuitable soil and dissection in trees forested areas and serious damages. The effects of mass movements on communication networks in several scientific disciplines were assessed. In addition, geo-morphologists and geologists studied the mechanism and the cause, the extent and number of landslides occurrence in various environments. Khorramabad-Pole Zaal freeway as a north-south transit highway, is one of the anfractuous mountain paths which is always in danger of road closure due to excessive expansion and various geo-morphological units. However, most risks that threatened this axis have often the geomorphological- climate origin which have created innumerous casualties and property damages due to of the lack engineering strategies and structures or counting non-significant the geomorphological parameters of present and future. The purpose of the slope stability analysis, is to offer appropriate safety coefficient providing stability. Therefore, recognizing the slope stability factor is necessary to prevent mitigation risks and damages.
2-Materials and Methods
As the first step, the slopes along the road were determined. After the determining the slopes and the sliding slopes, all the model parameters were checked and determined by field studies. Then the samples were delivered to the technical and soil mechanic laboratory. Kayasta (2006) and Vinh (2007) were used to measure and specify the root cohesion for the analyzed slopes. Besides, these measures were used for different land uses. The determined parameters included: c_s: soil cohesion, c_r: root cohesion, φ: internal friction angle of soil, γ_d: soil density and γ_w: wet density of soil. Determining these parameters, they were measured. Finally, the parameters were entered slope stability analysis to determine safety factor for each slope.
3-Results and Discussion
In this research, the stability of 8 sliding slopes along the roads was analyzed. One profile (to the depth of bedrock) was dug to measure each parameter in every profile. After delivering the samples to the soil laboratory, the essential parameters were measured to perform the slope stability model. Stability coefficient for slope number 6 is 0.57 and for the slope 8 is 1.17. As For the classification proposed by Peck et al. (1998), the slope  number 6 is located in the class of very high landslide invulnerability, while the slope number 8 is in the class of is high vulnerability. Due to the slope stability factor (FS) in range Case based on the slope stability analysis and compare it with the actual conditions, it can be concluded that the slops 2 and 5, according to the table (4) are put in a low instability class. In other words, these slopes are considered stable. (FS>1.5) and no slide could be observed the slops 1 and 4, in the class average vulnerability (1.25> FS>1.5). So it can be argued that these slopes may not slip by themselves in nature. However, some man-made factors such as road constructing have been effective on making slides in these slopes.
4-Conclusion
In this research, the stability of 8 sliding slopes along the freeway Khrmabad- Plzal was studied. Besides, sustainable ways were found using the softwareFLAC SLOP. Two types of protective mechanism (Nailing and Terracing) in a slope slide were modeled to increase the safety factor. The findings showed that computing stability factor of slopes we can detect the unstable slopes and some protective mechanism could be specified to increase the stability factor or factor of safety. Protective mechanism as nailing and tracing  increase the safety factor and reduce the driving forces protective mechanism as they can be decrease the stability of the slides prone to landslides. The results from nailing mechanism in the slope number (6) with a very high vulnerability class, increases the factor of safety from 0.57 to 1.98 and the terracing mechanism in the slope, increases the stability or safety factor at the value 2.10. And finally we can determine the best way to do the protective mechanism.